Sea water is not suitable for human consumption. Naturally present dissolved chemicals in sea water make it inconsumable. The precipitants and dissolved chemicals need to be separated from water to make it consumable. A combination of aeration system, filtration system, crystallizer, hydrophobic membrane carrying filter and pressure retarded osmosis system are used in various combination to desalinate the sea water. Pressure retarded osmosis process is also used to produce pressurized diluted brine which is further decompressed to by the turbine and used by the generators to produce electricity. Various heat exchange apparatus are used for energy conservation and efficient processing of water in a feasible way. The disclosure enables to purify water and provide an economical means for producing electricity.